1. Field of the Invention
This invention relates to a beam charge exchanging apparatus for converting a fast charged particle beam such as an ion beam into a neutral particle beam, the apparatus being employed in the manufacture of semiconductors or the like.
2. Prior Art
Conventionally, an apparatus shown in FIG. 7, which is known as a gas cell, has been widely used as a charge exchanging apparatus. The gas cell includes a gas container 6, which is placed in a vacuum container and includes holes 16 through which a charged particle beam is passed. The charged particle beam 1 which is passed through the gas container 6 collides with a gas 3, which is introduced in the gas container through a gas introducing pipe (not shown), whereby charges are exchanged between the charged particle beam and the gas. There is another conventional apparatus called a metallic vapor cell which employs an alkaline metallic vapor such as Li as a gas for the cell. In this apparatus, the charged particle beam 1 is passed through the vapor so as to cause the charged particle to collide with the metallic vapor, whereby charges are exchanged therebetween.
In the conventional gas cell, however, since gas 3 is introduced into the gas container 6 located in the vacuum container, the holes 16 of the gas container 6 should be made small to prevent the vacuum from deteriorating due to the diffusion of gas from the gas cell. For this reason, it has been impossible to obtain many gas particles or charged particles in the gas cell.
The metallic vapor cell has a similar drawback in that the quantity of beams introduced in the container is limited if the vacuum level is to be maintained has another drawback in that the container body is damaged by the chemically active alkaline metal.
According to the charge neutralizing method based on a molecular beam as disclosed in Japanese Patent Laid-Open Appln. No. 5-129096 which has recently been published, the charge exchanging efficiency is low because the number of molecules is limited and, therefore, it is difficult to accomplish a charge exchange for a large quantity of beams. Furthermore, using the aforesaid method to change a large quantity of ion beams into neutral beams requires a large apparatus. Hence, it has been difficult to obtain high-energy neutral particle beams effectively, and the highest possible energy value which could be obtained using this method is limited to a few KeV.
Furthermore, in the conventional charge exchanging apparatus, there was no means for immediately measuring the quantity of neutral particles after charge exchange.